Combustion engines, such as gas turbine engines in aircraft, typically work by turning chemical energy in fuel into mechanical or propulsive energy. This is generally done by injecting liquid fuel into a combustion chamber where it is vaporized and then mixed with air from the compressor section of the engine. Subsequent combustion of the reactive gaseous fuel-air mixture provides combustion products with high thermal energy which can subsequently be converted into propulsive forces and/or mechanical rotary shaft energy.
To vaporize and burn the fuel during the short residence time within the combustion chamber, it is ideal to atomize the liquid fuel stream into small droplets. These small droplets give the fuel a larger surface area to more quickly vaporize. This atomization can by done by using a hollow-cone injector such as the prefilming fuel injectors frequently used in propulsion and APU (Auxiliary Power Unit) gas turbine engines. Here, liquid fuel is admitted onto an annular surface. The fuel forms a film that is pulled along the surface by sheer forces from an airstream. At the edge of the surface, the film is discharged into the combustor volume. It stays as a film for a short period, eventually rupturing due to instabilities. At rupture, the film first forms ligaments and then small droplets, i.e., a droplet spray, ideal for vaporization.